Dampers of the features as above are known from the state of art as twin-tube dampers. They provide excellent tuning capabilities enabling for independent tuning both the valves of a slidable piston assembly and the valves of an additional base valve assembly that in a case of twin-tube dampers is located at the bottom end of the main tube. Twin-tube dampers also require relatively low pressure of the pressurised gas what results in relatively low internal pressure of the working liquid filling the damper, inducing relatively low friction force between a piston rod and a rod guide seal. Furthermore, the external tube is not used to guide the slidable piston assembly. Therefore possible deformations of the external tube, in particular in the bottom zone of the damper, where it is usually fixed to the steering knuckle of a vehicle suspension have no influence on the operation of the damper. Also the piston assembly is designed not to reach this bottom zone of the external tube in its sliding movement.
Nonetheless, twin-tube dampers also have some disadvantages due to their complex structure, such as inter alia the necessity to provide a base valve assembly and a rod guide of a construction enabling for support of the external tube.
These disadvantages of the twin tube dampers have been substantially eliminated in mono-tube dampers in which all three chambers, i.e. a rebound chamber, a compression chamber and a gas chamber, are arranged serially in a single tube. Mono-tube dampers are devoid of an additional valve assembly and an additional compensation chamber. A slidable partition is provided between the compression chamber and the gas chamber.
However, other problems arise. Higher pressure is required in the chambers of the damper to eliminate free displacement of a slidable partition with no damping force generated by the valves of the piston assembly (a so called “no damping stroke effect”). This increased pressure in turn requires an improved sealing of the piston rod guide which in turn generates higher friction forces between the piston rod and the rod guide seal. Furthermore, the damper's length is increased since the gas chamber is positioned in series with the compression chamber along the longitudinal axis of the damper. Moreover, a certain dead zone exists at the end of the gas chamber where possible deformations of the main tube (which in this case is also an external tube) might lead to jamming of the slidable partition or otherwise limiting its sliding movement. Finally mono-tube dampers often provide significantly limited tuning capabilities as compared to twin-tube dampers.
Yet another common disadvantage of both the above-mentioned damper types is a necessity to fill the gas chamber with a pressurised gas which process depends on the process of filing the damper with a working liquid.
It has been the object of the present invention to provide a hydraulic damper that would retain all the aforementioned advantages of a twin-tube damper along with simplicity of construction as provided by a mono-tube damper.
The inventors discovered that achieving these objects is possible by diverting the flow of working liquid radially inside the compression chamber (instead as radially outside as in twin-tube dampers).